Modern electronic devices utilize semiconductor components, commonly referred to as "integrated circuits," which incorporate numerous electronic elements. These chips are typically mounted on substrates that physically support the chips and electrically interconnect each chip with other elements of the circuit. The substrate may be part of a discrete chip package, such as a single chip module or a multi-chip module, or may be a circuit board. The chip module or circuit board is typically incorporated into a large circuit. An interconnection between the chip and the chip module is commonly referred to as a "first level" assembly or chip interconnection. An interconnection between the chip module and a printed circuit board or card is commonly referred to as a "second level" interconnection.
The structures utilized to provide the first level connection between the chip and the substrate must accommodate all of the required electrical interconnections to the chip. The number of connections to external circuit elements, commonly referred to as "input-output" or "I/O" connections, is determined by the structure and function of the chip.
The rapid evolution of the semiconductor art in recent years has created an intense demand for semiconductor chip packages having progressively greater numbers of contacts in a given amount of space. An individual chip may require hundreds or even thousands of contacts, all within the area of the front face of the chip. Certain complex semiconductor chips currently being used have contacts spaced apart from one another at center-to-center distances of 0.1 mm or less and, in some cases, 0.05 mm or less.
One method utilized to interconnect semiconductor chips having closely spaced contacts includes using anisotropic conductive material. In U.S. Pat. No. 5,627,405, issued May 6, 1997, Chillara discloses an integrated circuit assembly comprising an integrated circuit, a dielectric substrate and an anisotropic electrically conductive layer interposed between the dielectric substrate and the integrated circuit. The anisotropic electrically conductive layer is electrically conductive in directions that are parallel to an electrically conductive axis and is electrically insulative in other directions.
However, there continues to be a need for improvement in elements and methods of making anisotropic conductive elements for use in microelectronic packaging.